A. Field of the Invention
The present invention relates to mechanisms for actuating electrical switches in electrical circuits of the type employed for energizing various components of a mass-transit vehicle.
B. Description of the Prior Art
Mass transit vehicles often include a switch designated as a crew switch that is readily accessible to a crew member through the employment of key or similar device. The crew switch controls various components of the transit vehicles such as the warning lights, the doors, and automatic train operation of the vehicle in a coordinated train.
Typical prior art crew switches employ one or more sets of contacts that are opened and closed in response to the insertion and rotation of a key or similar device. An example of such a typical crew switch is illustrated in U.S. Pat. No. 3,561,160 assigned to the assignee of the present invention.
Prior art crew switches have the disadvantage of being susceptible to manipulation by a crew member to actuate one or more but not all of the electrical switches controlled by the crew switch. Consequently, critical and sometimes vital circuits are not energized by the crew member while other circuits are energized allowing the crew member to accomplish non-standard operation of the train or transit vehicle in a dangerous condition. For example, during maintenance of the transit vehicle, manipulation or "teasing" of the crew switch in order to establish local control can allow doors to open while the train is in motion. "Defeating" or non energization of warning light circuits designed to alert other crew members of non standard car operation can also occur resulting in operation of the transit vehicle without automatic control functions greatly increasing the probability of car collisions, and other situations resulting in personal injury and material damage.
Accordingly, it is desirable to provide a crew switch that is operative in one mode of operation or another and is incapable of being manipulated or "teased" into an intermediate position so as to energize some but not all of the electrical switches. At the same time, rugged construction capable of withstanding rough handling, adverse climatic conditions, vandalism, and other aspects of transit car operation over an extended period of time must be provided. As an indication of the extraordinary performance required in the transit industry, warrantees of eight years are commonly required on door operating systems. Vandalism, mentioned above, creates an additional and stringent requirement for a crew switch in that unauthorized operation must be prevented through key action. However, the key and operating mechanism must resist efforts to "pick" the switch, or more usually, destructive actions aimed at making the entire switch inoperative. One approach to providing such a crew switch is to include in the switch a cam and a resiliently biased cam follower wherein the cam includes large abutments or projections behind the cam follower. An example of this type of switch is illustrated in U.S. Pat. No. 2,794,103. This prior art switch is expensive due to the elaborate configuration of the cam and is susceptible of being manipulated or teased once the projections are worn to a degree such that a level surface on which the cam follower may sit is formed. Additionally, the construction and operating life would not meet transit car requirements as outlined above.
Another prior art procedure for preventing manipulation of a switch actuating mechanism includes a spring that serves to bias the switch to one mode of operation or the other. The switch must then be held in the different modes against the bias of the spring. This is accomplished by a locking apparatus such as a cam and cam follower. An example of this type of prior art switch is illustrated in U.S. Pat. No. 3,302,484. This type of prior art switch is expensive due to the employment of two torsion springs, a cam, and a cam follower and is bulky due to the several additional components. Operation of this switch in the transit car environment is also questionable.